The present invention relates to electrical terminals, methods of connecting an electrical wire to a terminal, electrical device assemblies and electrical device assembly methods.
Considerable difficulties have been encountered heretofore in making electrical circuit assemblies which include relatively fine wire leads. For example, wound wire coils typically incorporate a polymeric, plastic core and a fine wire, commonly referred to as "magnet wire," wound on the core. The wire normally has a coating of insulation. In manufacture of an electronic assembly including such a coil on a substrate such as a printed circuit board, an electrical connection must be established between the ends of the fine wire and metallic conductors on the circuit board. The coil must also be physically secured to the circuit board. Typically, the coil has been provided with a pair of elongated terminal pins. The pins are frictionally engaged in molded holes in the polymeric bobbin so that the pins extend transversely to the axis of the bobbin. The ends of the wire typically are wrapped around the pins and then soldered to the pins, as by immersing the pins in a solder bath. The pins are then positioned in holes in the circuit board, and soldered to the metallic lines on the circuit board as in a wave soldering operation.
Assembly procedures of this nature are costly and troublesome. The heat employed to solder the wires to the terminal pins and to solder the terminal pins to the circuit board may cause deformation of the polymeric bobbin and hence may cause loosening of the frictional engagement between the terminal pins and the bobbin. Also, the heat employed in soldering the terminal pins to the circuit board can cause melting of the solder at the wire to pin joints and hence may cause disconnection of the wire from the pins.
As set forth in the aforementioned U.S. Patent Application Ser. No. 808,530, the fine wires utilized in coils can be successfully fused to the terminal pins in a solderless fusing process. Each terminal pin is provided with notches or grooves sized to receive the wire and spaced along the length of the pin so that then the wire is wrapped onto the pin in a helical pattern, portions of the wire lie within the grooves. In one embodiment, the pins are substantially square in cross section, and the grooves extend across two opposed corners of the square cross section. Those portions of the wire which are received in the grooves are recessed relative to the outer surface of the pin. The pin is engaged with fusing electrodes so that the electrodes contact the pin in the vicinity of the grooves. Because the wire lodged within the grooves is recessed relative to the outer surface of the pin, the fusing electrodes do not contact the wire itself, but instead contact the pin. Ordinarily, two opposed electrodes contact each pin, and an electric current is passed between these electrodes through the pin, thereby heating the pin and wire to vaporize insulation from the wire and fuse the wire with the pin. Because the fusing electrodes contact the pin rather than the wire, a closed circuit is established between the electrodes even where the wire carries insulation. Moreover, the fusing electrodes cannot deform or sever the wire.
Terminal pins and fusing operations as described in the '530 application provide very significant improvements over the soldered wire to pin connections previously utilized Because the heat generated in the solderless fusing process is localized at the wire to pin junctures and typically is applied only for a brief moment, it does not tend to cause deformation of the bobbin. Moreover, the fused juncture between the wire and the pin will not be damaged by further heat applied in soldering the pin to the circuit board.
The teachings of the '530 application can also be applied in terminating leads from electronic and electrical devices other than coils, with similar advantages. Despite these advantages, even further improvement would be desirable.